Japan evacuated about 100,000 people from their homes yesterday, after rare torrential rains unleashed floods that left at least two people missing and stranded many more when rivers surged over their banks.

A further 800,000 people across eastern Japan have been advised to evacuate after officials issued pre-dawn warnings of unusually harsh rainfall to five million people.

Military helicopters plucked dozens of residents from the tops of their home, but rescue officials said they were unable to keep up with the pleas for help after raging floodwaters swamped parts of a city north of Tokyo.

The Kinugawa River broke through a flood berm, sending a wall of water into Joso, about 50km northeast of Japan's capital.

In one dramatic scene, the rescuer could be seen descending four times from a military helicopter over a 20-minute period to lift up four people one by one, as a deluge of water swept around their home.

Nearby, a man clung to a utility pole as the waters rose, before being taken up by a rescuer who had to be first lowered into the water so that he could make his way over to the man.

Others waved cloths from their deck as torrents of water washed away cars and knocked buildings off their foundations.

Japan's Kyodo news service reported that 39 people had been rescued by Japan's Self-Defence Forces, as its military is called, and rescue work was continuing.

There were no immediate reports of deaths or injuries.

However, as of yesterday evening, nine people were possibly missing because authorities could not reach them, city official Takao Kobayashi said. Authorities had rescued 70 of the 176 people who had requested help. Another 100 people were reported trapped on the second floor of a flooded supermarket, and 80 more in a nursing home.

The Transport Ministry estimated that 6,900 households have been affected by the flooding, Kyodo said, adding that only about 2,500 of the city's residents had been evacuated beforehand to shelters.

The floodwaters reached at least five miles from the breach.

Landslides

Troops were delivering food, blankets and water to about 780 people in several communities who were stranded but not seeking rescue.

The heavy rains also exacerbated a contaminated water problem at the crippled Fukushima nuclear plant as it overwhelmed the site's drainage pumps, sending radiation-tainted water into the ocean.

The rains came on the heels of Tropical Storm Etau, which caused flooding and landslides elsewhere on Wednesday as it crossed central Japan.

Yuko Kawamoto (58) said she decided to leave her home with her 80-year-old mother after watching TV images of the water pouring out of the embankment.